1. Field of the Invention
This invention relates to a thermoplastic laminated film with excellent adhesiveness, and in particular, to a thermoplastic laminated film with excellent adhesiveness to hydrophilic polymers, hydrophobic polymers, and inorganic substances.
2. Description of the Prior Art
Films made of thermoplastic resins such as polyester, polyamide, polypropylene, etc., and especially, films made of polyester such as polyethylene terephthalate, have excellent mechanical strength, heat-resistance, resistance to chemicals, translucency, and stability of dimensions. Therefore, such films have a wide variety of uses such as for the base film for magnetic tape, insulating tape, photographic film, tracing film, wrapping film for foodstuffs, and the like. However, these thermoplastic films ordinarily have poor adhesiveness to hydrophilic polymers, hydrophobic polymers, and inorganic substances. Accordingly, when this kind of film is coated with magnetic substances, photosensitive agents, matting agents, etc., the film surface should be treated by a corona discharge so that an anchor layer is provided. Also, when this kind of film is covered with a printed layer or a heat-sealable layer so that the film can be used for the wrapping of foodstuffs, the adhesion of the layer to the thermoplastic film is weak. Therefore, the strength of the heat seal, for example, is very weak.
In addition to the above methods for the improvement of the adhesiveness of thermoplastic films, other methods have been suggested for the treatment of the film by ultraviolet light, plasma discharge, flame treatment, corona discharge in a nitrogen atmosphere, and other physical methods. It is also possible to combine the use of these physical methods with chemical methods such as alkaline treatment, primer treatment, and the like. However, whatever the method is, the improvement achieved in the adhesiveness of the thermoplastic film is insufficient. In particular, the adhesiveness to hydrophilic polymers and hydrophobic polymers is unsatisfactory. Also, of the methods listed above, when that of primer treatment, in particular, is carried out, generally, the slipperiness of the film obtained is decreased, and therefore, operations such as rolling up of the film are made more difficult.